1. Field of the Invention
The present invention relates to a displacement detecting device that detects relative displacement between two members.
2. Description of the Related Art
In an industrial field, an instrument, such as an electronic caliper, is widely used for measuring a thickness of an object or other physical dimensions. A displacement detecting device (transducer) is used as one of the components forming the instrument. Of these known displacement detecting devices, an induction type of displacement detecting device detects a relative position between a detecting head, called a grid, and a scale by the utilization of an electromagnetic induction. In the displacement detecting device, current is fed to a magnetism generator contained in the detecting head so that a magnetic field is generated. The magnetic field generated is linked to a coil extending over the entire length of the scale, whereby the coil generates a voltage. The generated voltage is detected in the form of a signal by a magnetic flux sensor provided on the scale. The voltage induced in the magnetic flux sensor varies with a relative position between the detecting head and the scale. Accordingly, the relative position between the detecting head and the scale may be detected from the induced voltage signal. The displacement detecting device thus arranged needs two cables, one for feeding current to the detecting head and the other for transferring the signal from the scale. The work of separately connecting the cables to both the detecting head and the scale is troublesome.
In the displacement detecting device disclosed in Japanese Patent Unexamined Publication No. Hei. 10-318781 proposed by the applicant of the present patent application, only a magnetic flux coupling loop is provided on the scale. The magnetism generator and the magnetic flux sensor are both provided on the detecting head. A current feeding cable and a signal cable are bundled into a single cable, and the single cable is soldered to the detecting head. A primary magnetic flux generated by the magnetism generator of the detecting head induces a current in the magnetic flux coupling loop of the scale. The induced current generates a secondary magnetic flux. The secondary magnetic flux induces a voltage in a detecting coil of the magnetic flux sensor of the detecting head.
In the displacement detecting device arranged such that the scale is fixed to a fixing member, and the detecting head is fixed to a movable member, and a displacement of the detecting head relative to the scale is measured, the cable is bent with the movement of the detecting head. The bending of the cable possibly causes troubles, such as cable disconnection. The weight of the cable will hinder the operation of a high speed device, such as a linear-motor driven device. The conventional countermeasure for this problem is to frequently replace the cable with a new one, and to use a thin and tough cable. Unfortunately, this countermeasure is cumbersome for the user.
Accordingly, an object of the present invention is to provide a displacement detecting device that is free from the cable disconnection resulting from the movement of the detecting head, and does not hinder the high-speed operation of the device.
In accordance with the present invention, a displacement detecting device is provided for detecting a relative displacement between a first member and a second member. The first and second members, respectively, include output connectors for outputting a displacement signal on the basis of the relative displacement, and each output connector is fit to a common receiving-side connector.
In the displacement detecting device, at least one of the output connectors of the first or second members may be selected as a counterpart connector of the receiving-side connector, depending on the mounting space available. This feature provides several advantages when either of the first and second members, which is fixed in use, is connected to the receiving-side connector. One advantage is that there is no chance of the receiving-side cable for the receiving-side connector being disconnected by movement of the counterpart of the fixed member. This results in improvement of the reliability. An additional advantage is that the device is operable at high speed since the cable does not restrict motion of the movable member.
In the above-mentioned displacement detecting device, it is preferable that the first member include a displacement signal generating section for generating the displacement signal on the basis of the relative displacement and a transmitting circuit for transmitting the displacement signal. It is also preferable that the second member include a receiving circuit for receiving the displacement signal from the transmitting circuit.
The displacement signal generating section of the first member generates the displacement signal on the basis of the relative displacement. The displacement signal is transmitted to the second member by use of the transmitting circuit and the receiving circuit. In the displacement detecting device, the device construction is advantageously simplified. The signal transmission between the transmitting circuit and the receiving circuit may be made by use of non-contact transmitting means, which use a radio wave signal, an optical signal or the like. Contact transmitting means that use an electrical signal based on the electrical contact may be used in place of the non-contact transmitting means. The use of electromagnetic induction is more preferable. A wire communication may also be used for the data transmission between the first and second members within the scope of the invention.
In the above-mentioned displacement detecting device, it is also preferable that the first and second members each include displacement signal generating sections for generating the displacement signal based upon the relative displacement.
The first and second members each include displacement signal generating sections for generating the displacement signal on the basis of the relative displacement. Accordingly, the displacement signal may be derived from either of the displacement signal generating sections. This feature brings about the following advantages when either of the first and second members, which is fixed in use, is connected to the receiving-side connector. There is no chance that the receiving-side cable for the receiving-side connector will be disconnected by movement of the counterpart of the fixed member. This results in improvement of the reliability. Additionally, the device is operable at high speed since the cable does not restrict motion of the movable member.
In the above-mentioned displacement detecting device, it is preferable that at least one of the first and second members includes a power supplying section for supplying electric power from one of the first and second members to the other of the first and second members.
In the displacement detecting device, the power supplying section, which is provided on one of the two members, supplies electric power from one member to the other member. The other member is driven by the received electric power, and performs the displacement detecting operation. Accordingly, there is no need to use the cable for supplying electric power to the other member. The power supplying section may use the non-contact transmitting means based on electromagnetic induction or the contact transmitting means based on electrical contact. In either case, electrical power may be supplied in every attitude of the movable member before and after it is displaced. Further, the electrical power may be supplied to the movable member only when it takes a specific attitude.
In the above-mentioned displacement detecting device, it is preferable that each of the output connectors include a signal terminal and a power feeding terminal.
In the displacement detecting device, in a case where the receiving-side connector is connected to the output connector of the first member and also in a case were it is connected to the output connector of the second member, the electrical connection for outputting the displacement signal and the electrical connection for feeding electric power are made in one operation.
The above-mentioned object also can be achieved by a displacement detecting device for detecting a relative displacement between a detecting head and a scale extending over and confronted with the entire range of a locus representative of a movement of the detecting head. In accordance with the invention, the scale includes a connector incorporating therein an input terminal for feeding electric power to the detecting head and an output terminal for deriving a displacement signal from the detecting head.
In the displacement detecting device, when the receiving-side cable for the receiving-side connector is connected to the connector of the scale, the following advantages are obtained. There is no chance that the receiving-side cable will be disconnected by movement of the detecting head. This results in improvement of the reliability. Additionally, the device is operable at high speed since the cable does not restrict motion of the detecting head.
Further, the above-mentioned object can be achieved by a displacement detecting device for detecting a relative displacement between a first member and a second member, wherein the first member includes a displacement signal generating section for generating a displacement signal on the basis of the relative displacement and a signal transferring section for transferring the displacement signal to the second member. The first and second members, respectively, include input/output connectors. Each of the input/output connectors is configured so as to be fit to a common receiving-side connector and has an exciting terminal for receiving an exciting signal and a signal terminal for outputting the displacement signal on the basis of the relative displacement. The output of the displacement signal generating section is branched and connected to the signal terminal and the signal transferring section, respectively.
The displacement detecting device is used in a state that the receiving-side connector is connected to either of the input/output connectors of the first and second members. In a case where the receiving-side connector is connected to the input/output connector of the first member, when an exciting signal is input to the device through the exciting terminal of the input/output connector, the displacement signal generating section generates the displacement signal based on the relative displacement between the first and second members. The displacement signal is output from the signal terminal of the input/output connector to the receiving-side connector. In a case where the receiving-side connector is connected to the input/output connector of the second member, when the displacement signal generating section of the first member generates the displacement signal, the displacement signal is transferred to the second member by the signal transferring section, and output by the receiving-side connector.
In the displacement detecting device, the output of the displacement signal generating section of the first member is branched and connected to the signal terminal of the input/output connector of the first member and the signal transferring section, respectively. In a case where the receiving-side connector is connected to the input/output connector of the first member and, also, in a case where the receiving-side connector is connected to the input/output connector of the second member, the displacement signal may be output via the receiving-side connector. Accordingly, an exciting circuit for generating the exciting signal and a receiving circuit for processing the displacement signal may be provided on an outside member not fixed to the first and second members. As a result, the first and second members may be constructed to be extremely small in size and heavy duty. Further, the device maintenance is easy.